In a power transmission or distribution network, electrical switching apparatuses are incorporated into the network to provide automatic protection in response to abnormal load conditions or to permit opening or closing (switching) of sections of the network. The switching apparatus may therefore be called upon to perform a number of different operations such as interruption of terminal faults or short line faults, interruption of small inductive currents, interruption of capacitive currents, out-of-phase switching or no-load switching, all of which operations are well known to a person skilled in the art.
In switching apparatuses the actual opening or closing operation is carried out by at least two contacts, which are movable in relation one another, where normally one is stationary and the other is mobile. The mobile contact is operated by an operating system which may comprise a latching apparatus, e.g. controlled by an actuator, and a mechanical system, where said mechanical system operatively connects the latching apparatus to the mobile contact of the switching apparatus.
EP 2 001 031-A1 discloses a latch assembly for an electrical switching apparatus operating mechanism.
US 2009/0050605-A1 describes a circuit breaker having an automatic release linkage.
U.S. Pat. No. 6,008,459 discloses a molded plastic current limiting circuit breaker including an operating mechanism and an actuator.
U.S. Pat. No. 5,713,459 describes a roller latching and release mechanism for electrical switching apparatus.
U.S. Pat. No. 3,810,051 discloses a circuit breaker trip and latch mechanism.
EP 2 246 869-A1 discloses a mechanical latching unit for a main drive unit for an electrical switching apparatus. The latching unit comprises a first roller movable between a first position and a second position, in the first position the first roller being adapted to lock a drive tooth of the main drive unit in a locked position and a force of the drive tooth being applied to the first roller. In the second position the first roller is adapted to release the drive tooth from the locked position. The latching unit also comprises a counter roller, and in at least the first position the first roller is adapted to bear against the counter roller. The latching unit further comprises guiding grooves, a carriage and a locking lever for guiding the movement of the first roller. In the first position the first roller is adapted to distribute the force of the drive tooth, applied to the first roller, to a primary force component applied to the counter roller and a secondary force component applied to the carriage.
Requirements for latching apparatuses, especially when used for electrical switching apparatuses, are high reliability, resistance to shock and overload conditions, resistance to large temperature ranges, high repeatability with lowest possible scatter, and short and adjustable reaction time and total mechanical operation time. Typically these requirements and operating conditions imply a complex structure and high quality and consequently costly system designs.
If these latching apparatuses are designed to meet low cost targets usually there have to be compromises in quality and/or performance.